The present invention relates to alumina hydrate used as a filler for thermoplastic resins. More specifically, the invention concerns surface modification of alumina hydrate to render the hydrate compatible with thermoplastic resins.
Inorganic materials, such as alumina hydrates, talc and calcium carbonate, are frequently employed as fillers in thermoplastic resins, including polypropylene, polyethylene and polyvinyl chloride (rigid and flexible). The fillers can impart increased mechanical strength, stiffness and, in the case of alumina hydrate, increased flame retardancy and decreased smoke generation. Filled thermoplastic resins are widely used as molded components in automobiles, appliances and machine housings and as extruded components in sheet and tube form, for example, in wire and cable jacketing.
When alumina hydrates are added to thermoplastic resins in amounts needed to achieve a reasonable degree of flame retardancy (about 35 to 65 percent by weight), the hydrates can detrimentally influence physical properties even where uniformly dispersed. For example, when incorporated into polypropylene, they reduce flexibility and impact strength. Even more detrimental to physical properties is the difficulty of realizing uniform dispersions of alumina hydrate in the resins. Gross heterogeneities caused by undispersed agglomerates can seriously compromise physical properties, especially impact strength and cosmetic qualities, such as gloss and surface smoothness. Consequently, the use of alumina hydrate, which is otherwise an excellent and low cost flame retardant filler, is considered less desirable than other fillers for most applications where retention of physical properties is required.
It is a principal object of the present invention to provide powdered alumina hydrate with a surface coating that will cause filled thermoplastic compounds made with the hydrate to exhibit satisfactory flame retardancy and smoke suppressive qualities and improved final physical properties compared with thermoplastic compounds filled with an equivalent amount of unmodified alumina hydrate.
It is a related object of the invention to provide a surface modified alumina hydrate composition that possesses improved processing characteristics.
Additional objects and advantages of the invention will become apparent to persons skilled in the art from the following specification.